Various techniques have been used in the treatment of wastewater. U.S. Pat. No. 5,316,668 to Tang discloses a wastewater treatment plant comprising a pretreatment chamber, aeration chamber and a settling chamber designed to minimize or eliminate sludge buildup at the bottom of the aeration chamber. In Tang, two support walls are provided. The combined function of one support wall and an angular portion at the bottom of the common wall, between the aeration and settling chamber, regulates the flow pattern in the aeration chamber and returns settled biodegradable matter from the bottom of the settling chamber to the aeration chamber for further treatment. The fluid flow created by the wall structure enhances the action of the settling chamber and eliminates dead zones in the aeration chamber thus minimizing sludge buildup.
In another example of wastewater treatment, U.S. Pat. No. 5,484,524 to MacLaren et al. discloses a similar wastewater treatment plant for removal of organic matter. In this patent, suspended solids and other pollutants comprising a pre-treatment chamber, a biofilm-aeration chamber and a settling chamber. Biofilm grows on a biofilm support structure that is stationary and submerged in the mixed liquor of the biofilm aeration chamber. The combination of submerged or surface aeration and suspended solid particle size reduction occurs, thereby creating a sufficient fluid flow within the biofilm aeration chamber. In this combination of sufficient fluid flow and reduced particle size, suspended organic particles and pollutants are efficiently digested by the biofilm. This results in an effective digestive process that produces no sludge. Further, the resulting effluent has a high level of dissolved oxygen, which is desirable, as well as a low biochemical oxygen demand (BOD) and suspended solids (SS).
This type of treatment system provides effective wastewater treatment before effluent is discharged to an appropriate disposal area. This is essential, since in many parts of the country, disinfected effluent is discharged directly to open drainage ditches or streams. For example, the JET series 1500 treatment system, available from JET Inc. of 750 Alpha Dr. Cleveland, Ohio, is used in such applications. The JET system has been rigorously tested by the National Sanitation Foundation and found to achieve a NSF 40 Class 1 effluent quality, i.e., an effluent quality consistently better than 30 mg/L BOD and 30 mg/L total suspended solids (TSS). This system is particularly well suited for use where small lots, high groundwater, and/or poor soils are encountered.
In operation, the JET system utilizes a motor driven aspirator shaft that thoroughly mixes and disperses fine air bubbles into the aerobic chamber of the treatment tank. This is an activated sludge system, which uses both suspended and fixed growth bacteria to achieve secondary biological treatment. The aeration chamber capacity of 650 gallons for the above-mentioned JET system allows a detention time of more than 30 hours at design flow of 500 gallons per day. Larger systems can handle higher flows. The benefits of such systems include: superior effluent quality, dramatically reduced need for further wastewater treatment; reduced leaching area, or direct effluent discharge after disinfection; decreased separation to groundwater; effective use of poor soil conditions; and increased the life expectancy of the leach area due to discharge of high quality effluent.
In these types of wastewater treatment systems, the primary moving part is the motor driven aerator. If water enters the motor, it causes damage resulting in the need to repair the aerator or replace the system. Water damage can occur when the water level in the tank rises to a point where it contacts the aerator, which occurs most frequently when there is a blockage of the tank outlet. Although one method to avoid water damage caused by outlet blockage is the installation of an overflow valve, use of these valves is not always possible and, even when used, these valves are subject to blockage and can be overwhelmed by heavy flooding.
FIG. 1 shows a typical aerator design of the prior art. In this system there are multiple locations where leakage can occur, at sites 1–4. The seal 1 between the top enclosure and the top endbell is a major leak point in this type of aerator. During a flood of the plant, water rises through the aspirator, aspirator shaft and rotor shaft and spills over the top of the rotor shaft. The rubber disk that seals between the top enclosure and the top endbell does not seal around the rotor shaft. This provides an open path for liquid to run freely into the interior of the motor.
The thru bolts 2 are another leak point in this type of aerator. When liquid rises to the level of the top of the top endbell, liquid runs between the top enclosure and the top endbell and enters the cavities around the thru bolt heads and drains into the motor. Another area prone to leakage is the point 3 between the endbells and the stator shell. Yet another leak point is the lower seal 4. When the seal 4 wears down, as it always will, it will begin to leak air out of the air seal enclosure, negating the diving bell effect and providing another leak point.
What is needed is a water resistant aerator that resists leaking and water damage, making the aerator longer lasting, less prone to damage from blockage, and more resilient to wet environments.